Research On The Key Technologies Of Signal Processing In Distributed Optical Fiber Sensors

The state of the art of distributed optical fiber sensing technology has been introduced with particular attention to the distributed sensing based on Brillouin scattering. The temperature and strain dependences of Brillouin shift and intensity have been investigated theoretically. A BOTDR sensing system based on Landau-Placzek Ratio and microwave heterodyne detection has been researched and the signal processing scheme of the sensing system has been studied according to characteristics of Brillouin scattering signal. The acquisition and de-noising of Brillouin intensity simulation signal have been achieved in LabVIEW. According to the problems of cumulative average algorithm, a method of combining cumulative average with wavelet modulus has been proposed to shorten the system's measurement time and improve the system performance. The systematic schemes and measurement principles of double-pulse BOTDR sensing technology have been analyzed in detail. By performance simulation of double-pulse BOTDR sensing system, the high resolution measurement of temperature and strain information has been demodulated correctly. The simulation results showed that the double-pulse BOTDR sensing system can measure a distributed Brillouin frequency shift, i.e., the distributed strain and temperature, with a spatial resolution of 20 cm and accuracy of±20 strain. The sensing principles and measurement method of coherent OTDR sensing technology have been analyzed in detail. By numerical simulating of coherent OTDR sensing system, the correlation peak spectral bandwidth dependences of pulse width have been investigated, and the bandwidth of correlation peak spectra increases with pulse width increases. The simulation confirmed that the coherent OTDR sensing system can measure the distributed temperature and strain, with a resolution of 0.01℃and a spatial resolution of 1 m.